JP2014060063A - Power storage device and method for manufacturing electrodes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device that provides high adhesion between metal foil and an active material layer, and to provide a method for manufacturing electrodes.SOLUTION: A secondary battery 100 includes a case 10, and an electrode assembly 20 that is housed in the case 10. The electrode assembly 20 has a positive electrode 30, a negative electrode 40, and a separator 50 that is arranged between the positive electrode 30 and the negative electrode 40. The negative electrode 40 has metal foil 12, and an active material layer 14 that is provided on the metal foil 12 and that includes an active material 16 and a binder 18. An inner portion 14a of the active material layer 14 is lower in porosity than a surface portion 14b of the same, where the inner portion 14a is defined as a portion of the active material layer 14 extending upward from the metal foil 12 to a distance of one-third the thickness of the active material layer 14 and the surface portion 14b is defined as a portion of the active material layer 14 extending downward from a surface of the active material layer 14 to two-thirds the thickness of the active material layer 14.

Description

  The present invention relates to a power storage device and a method for manufacturing an electrode.

  A method of manufacturing an electrode of a secondary battery by applying a slurry containing a binder, an active material, and a solvent on a metal foil and then drying the slurry is known (see, for example, Patent Document 1).

JP 2012-94463 A

  By the above method, an active material layer containing an active material and a binder is formed on the metal foil. However, in the electrode, since the adhesion between the metal foil and the active material layer is not sufficient, the active material layer may be peeled off from the metal foil due to, for example, expansion or contraction of the active material accompanying charge / discharge.

  The present invention provides a power storage device having high adhesion between a metal foil and an active material layer, and a method for manufacturing an electrode.

  A power storage device according to one aspect of the present invention includes a case and an electrode assembly housed in the case, and the electrode assembly is between a positive electrode, a negative electrode, and the positive electrode and the negative electrode. A separator disposed therein, and the negative electrode includes a metal foil and an active material layer provided on the metal foil and including an active material and a binder. In the active material layer, from the metal foil When a portion up to 1/3 of the thickness of the active material layer is defined as an inner portion and a portion from the surface of the active material layer to 2/3 of the thickness of the active material layer is defined as a surface portion, The porosity of the inner part is smaller than the porosity of the surface part.

  For example, in the cross section in the thickness direction of the active material layer, the porosity is expressed as a ratio of the cross-sectional area of the void to the entire cross-sectional area of the active material layer and the void. In this power storage device, the binder density in the inner part located in the vicinity of the metal foil can be increased. As a result, since the adhesiveness between the metal foil and the active material layer is increased, the active material layer is difficult to peel from the metal foil.

The active material may include SiO _x (0.5 ≦ x ≦ 1.5).

An active material containing SiO _x (0.5 ≦ x ≦ 1.5) tends to expand or contract. Even in such a case, the active material layer is hardly peeled off from the metal foil in the power storage device.

  The ratio of the porosity of the surface portion to the porosity of the inner portion may be 1.8 to 2.4.

  When the ratio is 1.8 or more, the adhesion between the metal foil and the active material layer becomes higher. When the ratio is 2.4 or less, the production of the active material layer is facilitated.

  The power storage device may be a secondary battery.

  An electrode manufacturing method according to another aspect of the present invention includes a step of applying an electrode material including an active material, a binder, and a solvent on a metal foil, a step of irradiating the metal foil with ultrasonic waves, Forming an active material layer including the active material and the binder on the metal foil by drying the electrode material after irradiating the sound wave.

  In this method, the bubbles in the electrode material are moved away from the metal foil by irradiating the metal foil with ultrasonic waves. Therefore, the porosity of the part located in the vicinity of the metal foil in the active material layer can be reduced. As a result, since the adhesiveness between the metal foil and the active material layer is increased, the active material layer is difficult to peel from the metal foil.

  ADVANTAGE OF THE INVENTION According to this invention, the electrical storage apparatus with high adhesiveness of metal foil and an active material layer, and the manufacturing method of an electrode can be provided.

It is sectional drawing which shows typically the electrical storage apparatus which concerns on one Embodiment. It is sectional drawing along the II-II line of FIG. It is sectional drawing which shows typically the electrode of the electrical storage apparatus which concerns on one Embodiment. It is process sectional drawing which shows the manufacturing method of the electrode which concerns on one Embodiment. It is sectional drawing which shows typically the electrical storage apparatus which concerns on another embodiment. It is a figure which shows the example of the cross-sectional SEM photograph of an electrode. It is a graph which shows an example of the relationship between a discharge capacity maintenance factor and the number of cycles.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and redundant descriptions are omitted.

  FIG. 1 is a cross-sectional view schematically showing a power storage device according to one embodiment. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 and 2 is a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

  The secondary battery 100 includes a case 10 and an electrode assembly 20 accommodated in the case 10. The electrode assembly 20 includes a positive electrode 30, a negative electrode 40, and a separator 50 disposed between the positive electrode 30 and the negative electrode 40. The positive electrode 30, the negative electrode 40, and the separator 50 are, for example, a sheet shape. A plurality of positive electrodes 30 and a plurality of negative electrodes 40 may be alternately stacked via separators 50. The case 10 can be filled with the electrolytic solution 60.

  The positive electrode 30 may have a tab 30a formed at the edge. The tab 30a does not carry a positive electrode active material. The positive electrode 30 can be connected to the conductive member 32 via the tab 30a. The conductive member 32 can be connected to the positive terminal 34. The positive electrode terminal 34 may be attached to the case 10 via an insulating ring 36.

  The negative electrode 40 may have a tab 40a formed at the edge. The tab 40a does not carry a negative electrode active material. The negative electrode 40 can be connected to the conductive member 42 via the tab 40a. The conductive member 42 can be connected to the negative terminal 44. The negative electrode terminal 44 may be attached to the case 10 via the insulating ring 46.

  Examples of the separator 50 include a porous film made of a polyolefin resin such as polyethylene (PE) and polypropylene (PP), a woven fabric or a non-woven fabric made of polypropylene, polyethylene terephthalate (PET), methylcellulose, and the like.

  Examples of the electrolytic solution 60 include an organic solvent-based or non-aqueous electrolytic solution. The organic solvent-based electrolytic solution includes an organic solvent and an electrolyte. The non-aqueous electrolyte contains a polymer electrolyte. The organic solvent contained in the electrolytic solution 60 may contain a chain ester. Thereby, load characteristics are improved. Examples of the chain ester include a chain carbonate, an organic solvent such as ethyl acetate or methyl propionate, or a mixed solution thereof. Examples of the chain carbonate include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

  The electrolytic solution 60 may include a material that generates hydrogen when a predetermined current flows through the electrode assembly 20. Examples of the material that generates hydrogen include aromatic monomers. The aromatic monomer causes a polymerization reaction to generate hydrogen when a current of a predetermined value or more flows through the electrode assembly 20. Examples of aromatic monomers include thiophenes such as thiophene and 3-halogenated thiophene, alkylbenzenes such as 1,2-methoxybenzene, and 1-methyl-3- (pyrrol-1-ylmethyl) pyridinium tetrafluoroborate. Heterocyclic compounds, biphenyl, furan and the like are exemplified.

  FIG. 3 is a cross-sectional view schematically showing an electrode of the power storage device according to the embodiment. The electrode 1 shown in FIG. 3 is used as the negative electrode 40. The electrode 1 includes a metal foil 12 and an active material layer 14 provided on the metal foil 12. The metal foil 12 may be, for example, a copper foil, a nickel foil, an aluminum foil, a stainless steel foil, or the like. The thickness of the metal foil 12 is, for example, 10 to 20 μm. The thickness of the active material layer 14 may be 20 to 100 μm, for example 40 μm. The active material layer 14 includes an active material 16 and a binder 18. Examples of the constituent material of the binder 18 include a resin such as polyamideimide. The active material layer 14 may further include a conductive additive such as carbon black, graphite, acetylene black, ketjen black, and the like.

  The active material 16 is, for example, active material particles. The active material 16 is a negative electrode active material.

The active material 16 may include SiO _x (0.5 ≦ x ≦ 1.5) particles 16a. x may be 0.7 or more and 1.2 or less. The average particle diameter D50 of the SiO _x particles 16a may be 1 to 15 μm or 4 to 10 μm. The average particle diameter D50 is a particle diameter corresponding to a volume-based integrated value of 50% in the particle size distribution measurement by the laser diffraction / diffusion method.

  The active material 16 may include graphite particles 16b. The average particle diameter D50 of the graphite particles 16b may be 4 to 30 μm, 5 to 25 μm, or 8 to 20 μm. Examples of the graphite particles 16b include powders such as natural graphite powder, artificial graphite powder, spherulite graphite powder (graphitized mesophase carbon microspheres), and graphite carbon material powder. Examples of the graphite carbon material include thermal decomposition products of condensed polycyclic hydrocarbon compounds such as pitch and coke.

  A void 14 c may be formed in the active material layer 14. The maximum diameter of the gap 14 c may increase as the distance from the metal foil 12 increases. The maximum diameter of the gap 14c is, for example, half or less of the average particle diameter D50 of the graphite particles 16b.

  In the active material layer 14, a portion from the metal foil 12 to 1/3 of the thickness of the active material layer 14 is an inner portion 14 a, and the surface of the active material layer 14 is 2/3 of the thickness of the active material layer 14. When the portion up to the thickness is defined as the surface portion 14b, the porosity of the inner portion 14a is smaller than the porosity of the surface portion 14b.

  The ratio of the porosity of the surface portion 14b to the porosity of the inner portion 14a is, for example, 1.8 to 2.4. For example, in the cross section in the thickness direction of the active material layer 14, the porosity is represented by the ratio of the cross-sectional area of the void 14c to the entire cross-sectional area of the active material layer 14 and the void 14c. The cross section in the thickness direction of the active material layer 14 is obtained by cutting the active material layer 14 in the thickness direction by, for example, a cross section polisher method (CP method) using an argon ion beam. The cross section is observed by SEM, for example. The cross-sectional area of the gap 14c can be measured using an image processing apparatus.

  In the secondary battery 100, the density of the binder 18 in the inner part 14a located in the vicinity of the metal foil 12 can be increased. As a result, the adhesion between the metal foil 12 and the active material layer 14 is increased. Therefore, even if the volume of the active material 16 expands or contracts due to charge / discharge, for example, the active material layer 14 peels from the metal foil 12. It becomes difficult. As a result, the cycle life of the secondary battery 100 becomes longer and the deterioration of the high rate characteristic is suppressed.

The active material 16 including the SiO _x particles 16a is easily expanded or contracted. For example, the volume of the SiO _x particles 16a can expand about twice as much as charging and discharging. Even in such a case, in the secondary battery 100, the active material layer 14 is difficult to peel from the metal foil 12.

  When the ratio of the porosity of the surface portion 14b to the porosity of the inner portion 14a is 1.8 or more, the adhesion between the metal foil 12 and the active material layer 14 becomes higher. When the ratio is 2.4 or less, the active material layer 14 can be easily manufactured.

  FIG. 4 is a process cross-sectional view illustrating an electrode manufacturing method according to an embodiment. The electrode 1 shown in FIG. 3 is manufactured by the following method, for example.

  First, as shown in FIG. 4A, an electrode material 114 containing an active material 16, a binder 18, and a solvent is applied on the metal foil 12. The electrode material 114 is, for example, a paste or slurry. Bubbles 114 c may be generated in the electrode material 114. Examples of the solvent include organic solvents such as NMP (N-methylpyrrolidone), methanol, and methyl isobutyl ketone, and water.

  Next, as shown in FIG. 4B, the metal foil 12 is irradiated with ultrasonic waves. As a result, the bubbles 114 c generated in the electrode material 114 move away from the metal foil 12. In particular, the bubble 114c having a large maximum diameter is easy to move. Along with the movement of the bubble 114c, the plurality of bubbles 114c may be combined to generate a bubble 114c having a large maximum diameter. Furthermore, since cavitation is generated by ultrasonic waves, the compressive stress in the electrode material 114 increases. The ultrasonic waves are generated from an ultrasonic generator 70 such as an ultrasonic horn. The metal foil 12 coated with the electrode material 114 may be placed on the placement table 72. For example, ultrasonic waves generated from the ultrasonic generator 70 pass through the mounting table 72 and the metal foil 12 and reach the electrode material 114.

  The frequency of the ultrasonic wave is, for example, 19.5 kHz. The irradiation time of ultrasonic waves is, for example, 30 seconds. The amplitude of the ultrasonic wave of the ultrasonic generator 70 may be 5 to 50 μm, for example, 6.5 μm.

  In order to move the bubbles 114c, the metal foil 12 may be irradiated with electromagnetic waves. Further, the metal foil 12 may be rapidly heated. Furthermore, the electrode material 114 may include a material that generates gas by heating.

  Next, as shown in FIG. 4C, the active material layer 14 including the active material 16 and the binder 18 is formed on the metal foil 12 by drying the electrode material 114. For example, the electrode material 114 is dried by heating, and the solvent in the electrode material 114 is removed. The gap 14 c in the active material layer 14 is formed from bubbles 114 c in the electrode material 114. After the active material layer 14 is formed on the metal foil 12, the active material layer 14 and the metal foil 12 may be compression molded. Thereby, the adhesiveness of the active material layer 14 and the metal foil 12 further improves.

  In this method, the bubbles 114 c in the electrode material 114 move away from the metal foil 12 by irradiating the metal foil 12 with ultrasonic waves. Therefore, the porosity of the portion located in the vicinity of the metal foil 12 in the active material layer 14 can be reduced. As a result, since the adhesiveness between the metal foil 12 and the active material layer 14 is increased, the active material layer 14 is difficult to peel from the metal foil 12.

  FIG. 5 is a cross-sectional view schematically showing a power storage device according to another embodiment. A secondary battery 100a as a power storage device shown in FIG. 5 is a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery.

  In the secondary battery 100a, the positive electrode 30, the negative electrode 40, and the separator 50 are wound around the axis L. The positive electrode 30 can include a coated portion 30b where the positive electrode active material is coated and an uncoated portion 30c where the positive electrode active material is not coated. The negative electrode 40 can include a coated portion 40b where the negative electrode active material is coated and an uncoated portion 40c where the negative electrode active material is not coated. The electrode 1 shown in FIG. 3 is used as the negative electrode 40. In the secondary battery 100a, at least the same effects as the secondary battery 100 can be obtained.

  As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment.

  For example, as a power storage device including the electrode 1, in addition to the secondary batteries 100 and 100a, for example, an electric double layer capacitor may be used.

  For example, power storage devices such as the secondary batteries 100 and 100a may be mounted on the vehicle. Examples of the vehicle include an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric wheelchair, an electrically assisted bicycle, and an electric motorcycle.

(Example)
EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

  FIG. 6 is a diagram illustrating an example of a cross-sectional SEM photograph of an electrode. Fig.6 (a) shows the electrode of an Example. FIG.6 (b) shows the electrode of a comparative example. The electrode shown in FIG. 6A is an example of the electrode 1 in FIG. In FIG. 6A, the porosity of the inner portion 14a is 8%, and the porosity of the surface portion 14b is 17%. Therefore, the ratio of the porosity of the surface portion 14b to the porosity of the inner portion 14a is 2.1.

  FIG. 7 is a graph showing an example of the relationship between the discharge capacity maintenance rate and the number of cycles. In FIG. 7, data D <b> 1 shows the results of the electrode of the example in which the ratio of the porosity of the surface portion 14 b to the porosity of the inner portion 14 a is 2.16. Data D2 shows the results for the comparative electrode with a ratio of 0.9. As shown in FIG. 7, in the electrode of the example, when the number of cycles exceeds 100, a decrease in the discharge capacity retention rate is suppressed compared to the electrode of the comparative example.

  DESCRIPTION OF SYMBOLS 1 ... Electrode, 10 ... Case, 12 ... Metal foil, 14 ... Active material layer, 14a ... Inner part, 14b ... Surface part, 16 ... Active material, 18 ... Binder, 20 ... Electrode assembly, 30 ... Positive electrode, 40 ... Negative electrode, 50 ... separator, 100, 100a ... secondary battery, 114 ... electrode material.

Claims (5)

Case and
An electrode assembly housed in the case;
With
The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode,
The negative electrode includes a metal foil, and an active material layer provided on the metal foil and including an active material and a binder,
In the active material layer, a portion from the metal foil to 1/3 of the thickness of the active material layer is an inner portion, and the thickness of the active material layer from the surface of the active material layer is 2/3 of the thickness of the active material layer If the part up to this is defined as the surface part,
The power storage device, wherein the porosity of the inner portion is smaller than the porosity of the surface portion. The power storage device according to claim 1, wherein the active material includes SiO _x (0.5 ≦ x ≦ 1.5).   The power storage device according to claim 1 or 2, wherein a ratio of a porosity of the surface portion to a porosity of the inner portion is 1.8 to 2.4.   The power storage device according to claim 1, wherein the power storage device is a secondary battery. Applying an electrode material containing an active material, a binder, and a solvent on a metal foil;
Irradiating the metal foil with ultrasonic waves;
Forming an active material layer including the active material and the binder on the metal foil by drying the electrode material after irradiating the ultrasonic wave;
A method for producing an electrode, comprising: